1. Field of the invention
The present invention relates to a rechargeable battery. More particularly, the present invention relates to a battery module that improves cooling efficiency of unit cells.
2. Description of the Related Art
Unlike non-rechargeable batteries, rechargeable batteries may be repeatedly recharged. Low-capacity rechargeable batteries are used as a power source for various portable small electronic devices such as cellular phones, laptop computers, and camcorders. Large-capacity rechargeable batteries are used for motor-driven devices such as hybrid electric vehicles. Large-capacity rechargeable batteries can be formed by connecting multiple rechargeable batteries in series.
A typical battery module includes a plurality of rechargeable batteries, which are often referred to as unit cells (hereinafter “unit cells”). A unit cell includes an electrode assembly including positive and negative electrodes and a separator interposed therebetween, a case for housing the electrode assembly, a cap assembly combined with the case and sealing it, and positive and negative terminals electrically connected to the positive and negative electrodes, respectively.
The rechargeable batteries or unit cells are mainly formed in cylindrical or prismatic shape. When the unit cell is fabricated in a prismatic shape, the positive and negative terminals are mounted to externally protrude out of the cap assembly, so that they can be exposed outside the unit cell. When the unit cells forms a battery module, they are arranged such that the positive terminal of one unit cell is close to the negative terminals of an adjacent unit cell. Then, the positive and negative terminals are connected to each other through a conductor, which is fixed or fastened to the positive and negative terminals with nuts or other mechanisms.
A battery module is formed of several to tens of unit cells. The battery module is equipped with a cooling structure or mechanism for dissipating the heat generated from the unit cells and a circuit system for electrically controlling the unit cells. Furthermore, when the battery module is applied to a motor-driven device such as an electric cleaner, an electric scooter, or an automobile (an electric vehicle or a hybrid electric automobile), it needs many unit cells. The unit cells are usually arranged in a stacked structure, causing the battery module to have a large volume.
Therefore, it is difficult to down-size battery modules and an electrical device with such a large battery module. It is also difficult to evenly cool all the unit cells. In a typical battery device, a coolant circulates within a housing enclosing the aggregated unit cells. However, cooling may not be sufficient or effective to cool each unit cell evenly. When unit cells in a battery module are not evenly cooled, the performance of the battery module may deteriorate.
Furthermore, insufficiently cooled unit cells release heat, which may increase the temperature of the battery module and thereby may further deteriorate performance of the battery module. Particularly, this problem can be more serious in a battery module requiring high power.
The above information disclosed in this background section is only for the understanding of the background of the invention, and no statement in this section constitutes an admission of prior art.